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xfs_db(8) xfs_db(8)
NAME
xfs_db - debug an XFS filesystem
SYNOPSIS
xfs_db [ -c cmd ] ... [ -p prog ] [ -r ] [ -x ] xfs_special
xfs_db -f [ -c cmd ] ... [ -p prog ] [ -f ] [ -r ] [ -x ] file
DESCRIPTION
xfs_db is used to examine an XFS filesystem. Under rare circumstances
it can also be used to modify an XFS filesystem, but that task is nor-
mally left to xfs_repair(8) or to scripts such as xfs_admin that run
xfs_db.
The options to xfs_db are:
-c cmd xfs_db commands may be run interactively (the default) or as
arguments on the command line. Multiple -c arguments may be
given. The commands are run in the sequence given, then the
program exits. This is the mechanism used to implement
xfs_check(8).
-f Specifies that the filesystem image to be processed is stored
in a regular file (see the mkfs.xfs -d file option). This
might happen if an image copy of a filesystem has been made
into an ordinary file with xfs_copy(8).
-l Specifies the device special file where the filesystems
external log resides. Only for those filesystems which use
an external log. See the mkfs.xfs -l option, and refer to
xfs(5) for a detailed description of the XFS log.
-i Allows execution on a mounted filesystem, provided it is
mounted read-only. Useful for shell scripts such as
xfs_check(8), which must only operate on filesystems in a
guarenteed consistent state (either unmounted or mounted
read-only). These semantics are slightly different to that
of the -r option.
-p prog Set the program name for prompts and some error messages, the
default value is xfs_db.
-r Open file or xfs_special read-only. This option is required
if xfs_special is a mounted filesystem. It is only necessary
to omit this flag if a command that changes data (write,
blocktrash) is to be used.
-x Specifies expert mode. This enables the write command.
CONCEPTS
xfs_db commands can be broken up into two classes. Most commands are
for the navigation and display of data structures in the filesystem.
Other commands are for scanning the filesystem in some way.
Commands which are used to navigate the filesystem structure take argu-
ments which reflect the names of filesystem structure fields. There
can be multiple field names separated by dots when the underlying
structures are nested, as in C. The field names can be indexed (as an
array index) if the underlying field is an array. The array indices
can be specified as a range, two numbers separated by a dash.
xfs_db maintains a current address in the filesystem. The granularity
of the address is a filesystem structure. This can be a filesystem
block, an inode or quota (smaller than a filesystem block), or a direc-
tory block (could be larger than a filesystem block). There are a
variety of commands to set the current address. Associated with the
current address is the current data type, which is the structural type
of this data. Commands which follow the structure of the filesystem
always set the type as well as the address. Commands which examine
pieces of an individual file (inode) need the current inode to be set,
this is done with the inode command.
The current address/type information is actually maintained in a stack
that can be explicitly manipulated with the push, pop, and stack com-
mands. This allows for easy examination of a nested filesystem struc-
ture. Also, the last several locations visited are stored in a ring
buffer which can be manipulated with the forward, back, and ring com-
mands.
XFS filesystems are divided into a small number of allocation groups.
xfs_db maintains a notion of the current allocation group which is
manipulated by some commands. The initial allocation group is 0.
COMMANDS
Many commands have extensive online help. Use the help command for
more details on any command.
a See the addr command.
ablock filoff
Set current address to the offset filoff (a filesystem block
number) in the attribute area of the current inode.
addr [ field-expression ]
Set current address to the value of the field-expression.
This is used to ``follow'' a reference in one structure to
the object being referred to. If no argument is given the
current address is printed.
agf [ agno ]
Set current address to the AGF block for allocation group
agno. If no argument is given use the current allocation
group.
agfl [ agno ]
Set current address to the AGFL block for allocation group
agno. If no argument is given use the current allocation
group.
agi [ agno ]
Set current address to the AGI block for allocation group
agno. If no argument is given use the current allocation
group.
b See the back command.
back Move to the previous location in the position ring.
blockfree Free block usage information collected by the last execution
of the blockget command. This must be done before another
blockget command can be given, presumably with different
arguments than the previous one.
blockget [ -npsv ] [ -b bno ] ... [ -i ino ] ...
Get block usage and check filesystem consistency. The infor-
mation is saved for use by a subsequent blockuse, ncheck, or
blocktrash command. See xfs_check(8) for more information.
The -b option is used to specify filesystem block numbers
about which verbose information should be printed.
The -i option is used to specify inode numbers about which
verbose information should be printed.
The -n option is used to save pathnames for inodes visited,
this is used to support the xfs_ncheck(8) command. It also
means that pathnames will be printed for inodes that have
problems. This option uses a lot of memory so is not enabled
by default.
The -p option causes error messages to be prefixed with the
filesystem name being processed. This is useful if several
copies of xfs_db are run in parallel.
The -s option restricts output to severe errors only. This
is useful if the output is too long otherwise.
The -v option enables verbose output. Messages will be
printed for every block and inode processed.
blocktrash [ -n c ] [ -x a ] [ -y b ] [ -s s ] [ -0123 ] [ -t t ] ...
Trash randomly selected filesystem metadata blocks. Trashing
occurs to randomly selected bits in the chosen blocks. This
command is available only in debugging versions of xfs_db.
It is useful for testing xfs_repair(8) and xfs_check(8).
The -0, -1, -2, and -3 options (mutually exclusive) set the
operating mode for blocktrash. In -0 mode, changed bits are
cleared. In -1 mode, changed bits are set. In -2 mode,
changed bits are inverted. In -3 mode, changed bits are ran-
domized.
The -n option supplies the count of block-trashings to per-
form (default 1).
The -s option supplies a seed to the random processing.
The -t option gives a type of blocks to be selected for
trashing. Multiple -t options may be given. If no -t
options are given then all metadata types can be trashed.
The -x option sets the minimum size of bit range to be
trashed. The default value is 1.
The -y option sets the maximum size of bit range to be
trashed. The default value is 1024.
blockuse [ -n ] [ -c blockcount ]
Print usage for current filesystem block(s). For each block,
the type and (if any) inode are printed.
The -c option specifies a count of blocks to process. The
default value is 1 (the current block only).
The -n option specifies that file names should be printed.
The prior blockget command must have also specified the -n
option.
bmap [ -a ] [ -d ] [ block [ len ] ]
Show the block map for the current inode. The map display
can be restricted to an area of the file with the block and
len arguments. If block is given and len is omitted then 1
is assumed for len.
The -a and -d options are used to select the attribute or
data area of the inode, if neither option is given then both
areas are shown.
check See the blockget command.
convert type number [ type number ] ... type
Convert from one address form to another. The known types,
with alternate names, are: agblock or agbno (filesystem block
within an allocation group), agino or aginode (inode number
within an allocation group), agnumber or agno (allocation
group number), bboff or daddroff (byte offset in a daddr),
blkoff or fsboff or agboff (byte offset in a agblock or
fsblock), byte or fsbyte (byte address in filesystem), daddr
or bb (disk address, 512-byte blocks), fsblock or fsb or
fsbno (filesystem block, see the fsblock command), ino or
inode (inode number), inoidx or offset (index of inode in
filesystem block), and inooff or inodeoff (byte offset in
inode). Only conversions that ``make sense'' are allowed.
The compound form (with more than three arguments) is useful
for conversions such as convert agno ag agbno agb fsblock.
daddr [ d ]
Set current address to the daddr (512 byte block) given by d.
If no value for d is given the current address is printed,
expressed as a daddr. The type is set to data (uninter-
preted).
dblock filoff
Set current address to the offset filoff (a filesystem block
number) in the data area of the current inode.
debug [ flagbits ]
Set debug option bits. These are used for debugging xfs_db.
If no value is given for flagbits, print the current debug
option bits. These are for the use of the implementor.
dquot [ projectid_or_userid ]
Set current address to a project or user quota block.
echo [ arg ] ...
Echo the arguments to the output.
f See the forward command.
forward Move forward to the next entry in the position ring.
frag [ -adflqRrv ]
Get file fragmentation data. This prints information about
fragmentation of file data in the filesystem (as opposed to
fragmentation of freespace, for which see the freesp com-
mand). Every file in the filesystem is examined to see how
far from ideal its extent mappings are. A summary is printed
giving the totals.
The -v option sets verbosity, every inode has information
printed for it. The remaining options select which inodes
and extents are examined. If no options are given then all
are assumed set, otherwise just those given are enabled.
The -a option enables processing of attribute data.
The -d option enables processing of directory data.
The -f option enables processing of regular file data.
The -l option enables processing of symbolic link data.
The -q option enables processing of quota file data.
The -R option enables processing of realtime control file
data.
The -r option enables processing of realtime file data.
freesp [ -bcds ] [ -a a ] ... [ -e i ] [ -h h1 ] ... [ -m m ]
Summarize free space for the filesystem. The free blocks are
examined and totalled, and displayed in the form of a his-
togram, with a count of extents in each range of free extent
sizes.
The -a a option adds a to the list of allocation groups to be
processed. If no -a options are given then all allocation
groups are processed.
The -b option specifies that the histogram buckets are
binary-sized, with the starting sizes being the powers of 2.
The -c option specifies that freesp will search the by-size
(cnt) space Btree instead of the default by-block (bno) space
Btree.
The -d option specifies that every free extent will be
displayed.
The -e i option specifies that the histogram buckets are
equal-sized, with the size specified as i.
The -h h1 option specifies a starting block number for a his-
togram bucket as h1. Multiple -h options are given to spec-
ify the complete set of buckets.
The -m m option specifies that the histogram starting block
numbers are powers of m. This is the general case of -b.
The -s option specifies that a final summary of total free
extents, free blocks, and the average free extent size is
printed.
fsb See the fsblock command.
fsblock [ fsb ]
Set current address to the fsblock value given by fsb. If no
value for fsb is given the current address is printed,
expressed as an fsb. The type is set to data (uninter-
preted). XFS filesystem block numbers are computed ((agno <<
agshift) | agblock) where agshift depends on the size of an
allocation group. Use the convert command to convert to and
from this form. Block numbers given for file blocks (for
instance from the bmap command) are in this form.
hash string
Prints the hash value of string using the hash function of
the XFS directory and attribute implementation.
help [ command ]
Print help for one or all commands.
inode [ inode# ]
Set the current inode number. If no inode# is given, print
the current inode number.
label [ label ]
Set the filesystem label. The filesystem label can be used
by mount(8) instead of using a device special file. The max-
imum length of an XFS label is 12 characters - use of a
longer label will result in truncation and a warning will be
issued. If no label is given, the current filesystem label
is printed.
log [ stop | start filename ]
Start logging output to filename, stop logging, or print the
current logging status.
ncheck [ -s ] [ -i ino ] ...
Print name-inode pairs. A blockget -n command must be run
first to gather the information.
The -i option specifies an inode number to be printed. If no
-i options are given then all inodes are printed.
The -s option specifies that only setuid and setgid files are
printed.
p See the print command.
pop Pop location from the stack.
print [ field-expression ] ...
Print field values. If no argument is given, print all
fields in the current structure.
push [ command ]
Push location to the stack. If command is supplied, set the
current location to the results of command after pushing the
old location.
q See the quit command.
quit Exit xfs_db.
ring [ index ]
Show position ring (if no index argument is given), or move
to a specific entry in the position ring given by index.
sb [ agno ]
Set current address to SB header in allocation group agno.
If no agno is given use the current allocation group number.
source source-file
Process commands from source-file. source commands can be
nested.
stack View the location stack.
type [ type ]
Set the current data type to type. If no argument is given,
show the current data type. The possible data types are:
agf, agfl, agi, attr, bmapbta, bmapbtd, bnobt, cntbt, data,
dir, dir2, dqblk, inobt, inode, log, rtbitmap, rtsummary, sb,
symlink, and text. See the TYPES section below for more
information on these data types.
uuid [ uuid or generate or rewrite ]
Set the filesystem universally unique identifier (UUID). The
filesystem UUID can be used by mount(8) instead of using a
device special file. The uuid can be set directly to the
desired UUID, or it can be automatically generated using the
generate option. These options will both write the UUID into
every copy of the superblock in the filesystem. rewrite
copies the current UUID from the primary superblock to all
secondary copies of the superblock. If no argument is given,
the current filesystem UUID is printed.
version [ feature | [versionnum features2 ] ]
Enable selected features for a filesystem (certain features
can be enabled on an unmounted filesystem, after mkfs.xfs(8)
has created the filesystem). Support for unwritten extents
can be enabled using the extflg option. Support for version
2 log format can be enabled using the log2 option. Support
for extended attributes can be enabled using the attr1 or
attr2 option. Once enabled, extended attributes cannot be
disabled, but the user may toggle between attr1 and attr2 at
will (older kernels may not support the newer version).
With one argument, this command will write the updated ver-
sion number into every copy of the superblock in the filesys-
tem. If no argument is given, the current version and fea-
ture bits are printed. If two arguments are given, they will
be used as numeric values for the versionnum and features2
bits respectively, and their string equivalent reported (but
no modifications are made).
write [ field or value ] ...
Write a value to disk. Specific fields can be set in struc-
tures (struct mode), or a block can be set to data values
(data mode), or a block can be set to string values (string
mode, for symlink blocks). The operation happens immedi-
ately: there is no buffering.
Struct mode is in effect when the current type is structural,
i.e. not data. For struct mode, the syntax is ``write field
value''.
Data mode is in effect when the current type is data. In
this case the contents of the block can be shifted or rotated
left or right, or filled with a sequence, a constant value,
or a random value. In this mode write with no arguments
gives more information on the allowed commands.
TYPES
This section gives the fields in each structure type and their mean-
ings. Note that some types of block cover multiple actual structures,
for instance directory blocks.
agf The AGF block is the header for block allocation information;
it is in the second 512-byte block of each allocation group.
The following fields are defined:
magicnum: AGF block magic number, 0x58414746 ('XAGF')
versionnum: version number, currently 1
seqno: sequence number starting from 0
length: size in filesystem blocks of the allocation group.
All allocation groups except the last one of the filesystem
have the superblock's agblocks value here
bnoroot: block number of the root of the Btree holding free
space information sorted by block number
cntroot: block number of the root of the Btree holding free
space information sorted by block count
bnolevel: number of levels in the by-block-number Btree
cntlevel: number of levels in the by-block-count Btree
flfirst: index into the AGFL block of the first active entry
fllast: index into the AGFL block of the last active entry
flcount: count of active entries in the AGFL block
freeblks: count of blocks represented in the freespace Btrees
longest: longest free space represented in the freespace
Btrees
agfl The AGFL block contains block numbers for use of the block
allocator; it is in the fourth 512-byte block of each alloca-
tion group. Each entry in the active list is a block number
within the allocation group that can be used for any purpose
if space runs low. The AGF block fields flfirst, fllast, and
flcount designate which entries are currently active. Entry
space is allocated in a circular manner within the AGFL
block. Fields defined:
bno: array of all block numbers. Even those which are not
active are printed
agi The AGI block is the header for inode allocation information;
it is in the third 512-byte block of each allocation group.
Fields defined:
magicnum: AGI block magic number, 0x58414749 ('XAGI')
versionnum: version number, currently 1
seqno: sequence number starting from 0
length: size in filesystem blocks of the allocation group
count: count of inodes allocated
root: block number of the root of the Btree holding inode
allocation information
level: number of levels in the inode allocation Btree
freecount: count of allocated inodes that are not in use
newino: last inode number allocated
dirino: unused
unlinked: an array of inode numbers within the allocation
group. The entries in the AGI block are the heads of lists
which run through the inode next_unlinked field. These
inodes are to be unlinked the next time the filesystem is
mounted
attr An attribute fork is organized as a Btree with the actual
data embedded in the leaf blocks. The root of the Btree is
found in block 0 of the fork. The index (sort order) of the
Btree is the hash value of the attribute name. All the
blocks contain a blkinfo structure at the beginning, see type
dir for a description. Nonleaf blocks are identical in for-
mat to those for version 1 and version 2 directories, see
type dir for a description. Leaf blocks can refer to
``local'' or ``remote'' attribute values. Local values are
stored directly in the leaf block. Remote values are stored
in an independent block in the attribute fork (with no struc-
ture). Leaf blocks contain the following fields:
hdr: header containing a blkinfo structure info (magic number
0xfbee), a count of active entries, usedbytes total bytes of
names and values, the firstused byte in the name area, holes
set if the block needs compaction, and array freemap as for
dir leaf blocks
entries: array of structures containing a hashval, nameidx
(index into the block of the name), and flags incomplete,
root, and local
nvlist: array of structures describing the attribute names
and values. Fields always present: valuelen (length of value
in bytes), namelen, and name. Fields present for local val-
ues: value (value string). Fields present for remote values:
valueblk (fork block number of containing the value).
bmapbt Files with many extents in their data or attribute fork will
have the extents described by the contents of a Btree for
that fork, instead of being stored directly in the inode.
Each bmap Btree starts with a root block contained within the
inode. The other levels of the Btree are stored in filesys-
tem blocks. The blocks are linked to sibling left and right
blocks at each level, as well as by pointers from parent to
child blocks. Each block contains the following fields:
magic: bmap Btree block magic number, 0x424d4150 ('BMAP')
level: level of this block above the leaf level
numrecs: number of records or keys in the block
leftsib: left (logically lower) sibling block, 0 if none
rightsib: right (logically higher) sibling block, 0 if none
recs: [leaf blocks only] array of extent records. Each
record contains startoff, startblock, blockcount, and extent-
flag (1 if the extent is unwritten)
keys: [nonleaf blocks only] array of key records. These are
the first key value of each block in the level below this
one. Each record contains startoff
ptrs: [nonleaf blocks only] array of child block pointers.
Each pointer is a filesystem block number to the next level
in the Btree
bnobt There is one set of filesystem blocks forming the by-block-
number allocation Btree for each allocation group. The root
block of this Btree is designated by the bnoroot field in the
coresponding AGF block. The blocks are linked to sibling
left and right blocks at each level, as well as by pointers
from parent to child blocks. Each block has the following
fields:
magic: BNOBT block magic number, 0x41425442 ('ABTB')
level: level number of this block, 0 is a leaf
numrecs: number of data entries in the block
leftsib: left (logically lower) sibling block, 0 if none
rightsib: right (logically higher) sibling block, 0 if none
recs: [leaf blocks only] array of freespace records. Each
record contains startblock and blockcount
keys: [nonleaf blocks only] array of key records. These are
the first value of each block in the level below this one.
Each record contains startblock and blockcount
ptrs: [nonleaf blocks only] array of child block pointers.
Each pointer is a block number within the allocation group to
the next level in the Btree
cntbt There is one set of filesystem blocks forming the by-block-
count allocation Btree for each allocation group. The root
block of this Btree is designated by the coresponding AGF
block. The blocks are linked to sibling left and right
blocks at each level, as well as by pointers from parent to
child blocks. Each block has the following fields:
magic: CNTBT block magic number, 0x41425443 ('ABTC')
level: level number of this block, 0 is a leaf
numrecs: number of data entries in the block
leftsib: left (logically lower) sibling block, 0 if none
rightsib: right (logically higher) sibling block, 0 if none
recs: [leaf blocks only] array of freespace records. Each
record contains startblock and blockcount
keys: [nonleaf blocks only] array of key records. These are
the first value of each block in the level below this one.
Each record contains blockcount and startblock
ptrs: [nonleaf blocks only] array of child block pointers.
Each pointer is a block number within the allocation group to
the next level in the Btree
data User file blocks, and other blocks whose type is unknown,
have this type for display purposes in xfs_db. The block
data is displayed in hexadecimal format.
dir A version 1 directory is organized as a Btree with the direc-
tory data embedded in the leaf blocks. The root of the Btree
is found in block 0 of the file. The index (sort order) of
the Btree is the hash value of the entry name. All the
blocks contain a blkinfo structure at the beginning with the
following fields:
forw: next sibling block
back: previous sibling block
magic: magic number for this block type
The nonleaf (node) blocks have the following fields:
hdr: header containing a blkinfo structure info (magic number
0xfebe), the count of active entries, and the level of this
block above the leaves
btree: array of entries containing hashval and before fields.
The before value is a block number within the directory file
to the child block, the hashval is the last hash value in
that block
The leaf blocks have the following fields:
hdr: header containing a blkinfo structure info (magic number
0xfeeb), the count of active entries, namebytes (total name
string bytes), holes flag (block needs compaction), and
freemap (array of base, size entries for free regions)
entries: array of structures containing hashval, nameidx
(byte index into the block of the name string), and namelen
namelist: array of structures containing inumber and name
dir2 A version 2 directory has four kinds of blocks. Data blocks
start at offset 0 in the file. There are two kinds of data
blocks: single-block directories have the leaf information
embedded at the end of the block, data blocks in multi-block
directories do not. Node and leaf blocks start at offset
32GiB (with either a single leaf block or the root node
block). Freespace blocks start at offset 64GiB. The node
and leaf blocks form a Btree, with references to the data in
the data blocks. The freespace blocks form an index of
longest free spaces within the data blocks.
A single-block directory block contains the following fields:
bhdr: header containing magic number 0x58443242 ('XD2B') and
an array bestfree of the longest 3 free spaces in the block
(offset, length)
bu: array of union structures. Each element is either an
entry or a freespace. For entries, there are the following
fields: inumber, namelen, name, and tag. For freespace,
there are the following fields: freetag (0xffff), length, and
tag. The tag value is the byte offset in the block of the
start of the entry it is contained in
bleaf: array of leaf entries containing hashval and address.
The address is a 64-bit word offset into the file
btail: tail structure containing the total count of leaf
entries and stale count of unused leaf entries
A data block contains the following fields:
dhdr: header containing magic number 0x58443244 ('XD2D') and
an array bestfree of the longest 3 free spaces in the block
(offset, length)
du: array of union structures as for bu
Leaf blocks have two possible forms. If the Btree consists
of a single leaf then the freespace information is in the
leaf block, otherwise it is in separate blocks and the root
of the Btree is a node block. A leaf block contains the fol-
lowing fields:
lhdr: header containing a blkinfo structure info (magic num-
ber 0xd2f1 for the single leaf case, 0xd2ff for the true
Btree case), the total count of leaf entries, and stale count
of unused leaf entries
lents: leaf entries, as for bleaf
lbests: [single leaf only] array of values which represent
the longest freespace in each data block in the directory
ltail: [single leaf only] tail structure containing bestcount
count of lbests
A node block is identical to that for types attr and dir.
A freespace block contains the following fields:
fhdr: header containing magic number 0x58443246 ('XD2F'),
firstdb first data block number covered by this freespace
block, nvalid number of valid entries, and nused number of
entries representing real data blocks
fbests: array of values as for lbests
dqblk The quota information is stored in files referred to by the
superblock uquotino and pquotino fields. Each filesystem
block in a quota file contains a constant number of quota
entries. The quota entry size is currently 136 bytes, so
with a 4KiB filesystem block size there are 30 quota entries
per block. The dquot command is used to locate these entries
in the filesystem. The file entries are indexed by the user
or project identifier to determine the block and offset.
Each quota entry has the following fields:
magic: magic number, 0x4451 ('DQ')
version: version number, currently 1
flags: flags, values include 0x01 for user quota, 0x02 for
project quota
id: user or project identifier
blk_hardlimit: absolute limit on blocks in use
blk_softlimit: preferred limit on blocks in use
ino_hardlimit: absolute limit on inodes in use
ino_softlimit: preferred limit on inodes in use
bcount: blocks actually in use
icount: inodes actually in use
itimer: time when service will be refused if soft limit is
violated for inodes
btimer: time when service will be refused if soft limit is
violated for blocks
iwarns: number of warnings issued about inode limit viola-
tions
bwarns: number of warnings issued about block limit viola-
tions
rtb_hardlimit: absolute limit on realtime blocks in use
rtb_softlimit: preferred limit on realtime blocks in use
rtbcount: realtime blocks actually in use
rtbtimer: time when service will be refused if soft limit is
violated for realtime blocks
rtbwarns: number of warnings issued about realtime block
limit violations
inobt There is one set of filesystem blocks forming the inode allo-
cation Btree for each allocation group. The root block of
this Btree is designated by the root field in the corespond-
ing AGI block. The blocks are linked to sibling left and
right blocks at each level, as well as by pointers from par-
ent to child blocks. Each block has the following fields:
magic: INOBT block magic number, 0x49414254 ('IABT')
level: level number of this block, 0 is a leaf
numrecs: number of data entries in the block
leftsib: left (logically lower) sibling block, 0 if none
rightsib: right (logically higher) sibling block, 0 if none
recs: [leaf blocks only] array of inode records. Each record
contains startino allocation-group relative inode number,
freecount count of free inodes in this chunk, and free
bitmap, LSB corresponds to inode 0
keys: [nonleaf blocks only] array of key records. These are
the first value of each block in the level below this one.
Each record contains startino
ptrs: [nonleaf blocks only] array of child block pointers.
Each pointer is a block number within the allocation group to
the next level in the Btree
inode Inodes are allocated in ``chunks'' of 64 inodes each. Usu-
ally a chunk is multiple filesystem blocks, although there
are cases with large filesystem blocks where a chunk is less
than one block. The inode Btree (see inobt above) refers to
the inode numbers per allocation group. The inode numbers
directly reflect the location of the inode block on disk.
Use the inode command to point xfs_db to a specific inode.
Each inode contains four regions: core, next_unlinked, u, and
a. core contains the fixed information. next_unlinked is
separated from the core due to journaling considerations, see
type agi field unlinked. u is a union structure that is dif-
ferent in size and format depending on the type and represen-
tation of the file data (``data fork''). a is an optional
union structure to describe attribute data, that is different
in size, format, and location depending on the presence and
representation of attribute data, and the size of the u data
(``attribute fork''). xfs_db automatically selects the
proper union members based on information in the inode.
The following are fields in the inode core:
magic: inode magic number, 0x494e ('IN')
mode: mode and type of file, as described in chmod(2),
mknod(2), and stat(2)
version: inode version, 1 or 2
format: format of u union data (0: xfs_dev_t, 1: local file -
in-inode directory or symlink, 2: extent list, 3: Btree root,
4: unique id [unused])
nlinkv1: number of links to the file in a version 1 inode
nlinkv2: number of links to the file in a version 2 inode
projid: owner's project id (version 2 inode only)
uid: owner's user id
gid: owner's group id
atime: time last accessed (seconds and nanoseconds)
mtime: time last modified
ctime: time created or inode last modified
size: number of bytes in the file
nblocks: total number of blocks in the file including indi-
rect and attribute
extsize: basic/minimum extent size for the file
nextents: number of extents in the data fork
naextents: number of extents in the attribute fork
forkoff: attribute fork offset in the inode, in 64-bit words
from the start of u
aformat: format of a data (1: local attribute data, 2: extent
list, 3: Btree root)
dmevmask: DMAPI event mask
dmstate: DMAPI state information
newrtbm: file is the realtime bitmap and is ``new'' format
prealloc: file has preallocated data space after EOF
realtime: file data is in the realtime subvolume
gen: inode generation number
The following fields are in the u data fork union:
bmbt: bmap Btree root. This looks like a bmapbtd block with
redundant information removed
bmx: array of extent descriptors
dev: dev_t for the block or character device
sfdir: shortform (in-inode) version 1 directory. This con-
sists of a hdr containing the parent inode number and a count
of active entries in the directory, followed by an array list
of hdr.count entries. Each such entry contains inumber,
namelen, and name string
sfdir2: shortform (in-inode) version 2 directory. This con-
sists of a hdr containing a count of active entries in the
directory, an i8count of entries with inumbers that don't fit
in a 32-bit value, and the parent inode number, followed by
an array list of hdr.count entries. Each such entry contains
namelen, a saved offset used when the directory is converted
to a larger form, a name string, and the inumber
symlink: symbolic link string value
The following fields are in the a attribute fork union if it
exists:
bmbt: bmap Btree root, as above
bmx: array of extent descriptors
sfattr: shortform (in-inode) attribute values. This consists
of a hdr containing a totsize (total size in bytes) and a
count of active entries, followed by an array list of
hdr.count entries. Each such entry contains namelen, value-
len, root flag, name, and value
log Log blocks contain the journal entries for XFS. It's not
useful to examine these with xfs_db, use xfs_logprint(8)
instead.
rtbitmap If the filesystem has a realtime subvolume, then the rbmino
field in the superblock refers to a file that contains the
realtime bitmap. Each bit in the bitmap file controls the
allocation of a single realtime extent (set == free). The
bitmap is processed in 32-bit words, the LSB of a word is
used for the first extent controlled by that bitmap word.
The atime field of the realtime bitmap inode contains a
counter that is used to control where the next new realtime
file will start.
rtsummary If the filesystem has a realtime subvolume, then the rsumino
field in the superblock refers to a file that contains the
realtime summary data. The summary file contains a two-
dimensional array of 16-bit values. Each value counts the
number of free extent runs (consecutive free realtime
extents) of a given range of sizes that starts in a given
bitmap block. The size ranges are binary buckets (low size
in the bucket is a power of 2). There are as many size
ranges as are necessary given the size of the realtime sub-
volume. The first dimension is the size range, the second
dimension is the starting bitmap block number (adjacent
entries are for the same size, adjacent bitmap blocks).
sb There is one sb (superblock) structure per allocation group.
It is the first disk block in the allocation group. Only the
first one (block 0 of the filesystem) is actually used; the
other blocks are redundant information for xfs_repair(8) to
use if the first superblock is damaged. Fields defined:
magicnum: superblock magic number, 0x58465342 ('XFSB')
blocksize: filesystem block size in bytes
dblocks: number of filesystem blocks present in the data sub-
volume
rblocks: number of filesystem blocks present in the realtime
subvolume
rextents: number of realtime extents that rblocks contain
uuid: unique identifier of the filesystem
logstart: starting filesystem block number of the log (jour-
nal). If this value is 0 the log is ``external''
rootino: root inode number
rbmino: realtime bitmap inode number
rsumino: realtime summary data inode number
rextsize: realtime extent size in filesystem blocks
agblocks: size of an allocation group in filesystem blocks
agcount: number of allocation groups
rbmblocks: number of realtime bitmap blocks
logblocks: number of log blocks (filesystem blocks)
versionnum: filesystem version information. This value is
currently 1, 2, 3, or 4 in the low 4 bits. If the low bits
are 4 then the other bits have additional meanings. 1 is the
original value. 2 means that attributes were used. 3 means
that version 2 inodes (large link counts) were used. 4 is
the bitmask version of the version number. In this case, the
other bits are used as flags (0x0010: attributes were used,
0x0020: version 2 inodes were used, 0x0040: quotas were used,
0x0080: inode cluster alignment is in force, 0x0100: data
stripe alignment is in force, 0x0200: the shared_vn field is
used, 0x1000: unwritten extent tracking is on, 0x2000: ver-
sion 2 directories are in use)
sectsize: sector size in bytes, currently always 512. This
is the size of the superblock and the other header blocks
inodesize: inode size in bytes
inopblock: number of inodes per filesystem block
fname: obsolete, filesystem name
fpack: obsolete, filesystem pack name
blocklog: log2 of blocksize
sectlog: log2 of sectsize
inodelog: log2 of inodesize
inopblog: log2 of inopblock
agblklog: log2 of agblocks (rounded up)
rextslog: log2 of rextents
inprogress: mkfs.xfs(8) aborted before completing this
filesystem
imax_pct: maximum percentage of filesystem space used for
inode blocks
icount: number of allocated inodes
ifree: number of allocated inodes that are not in use
fdblocks: number of free data blocks
frextents: number of free realtime extents
uquotino: user quota inode number
pquotino: project quota inode number; this is currently
unused
qflags: quota status flags (0x01: user quota accounting is
on, 0x02: user quota limits are enforced, 0x04: quotacheck
has been run on user quotas, 0x08: project quota accounting
is on, 0x10: project quota limits are enforced, 0x20: quo-
tacheck has been run on project quotas)
flags: random flags. 0x01: only read-only mounts are allowed
shared_vn: shared version number (shared readonly filesys-
tems)
inoalignmt: inode chunk alignment in filesystem blocks
unit: stripe or RAID unit
width: stripe or RAID width
dirblklog: log2 of directory block size (filesystem blocks)
symlink Symbolic link blocks are used only when the symbolic link
value does not fit inside the inode. The block content is
just the string value. Bytes past the logical end of the
symbolic link value have arbitrary values.
text User file blocks, and other blocks whose type is unknown,
have this type for display purposes in xfs_db. The block
data is displayed in two columns: Hexadecimal format and
printable ASCII chars.
DIAGNOSTICS
Many messages can come from the check (blockget) command; these are
documented in xfs_check(8).
SEE ALSO
mkfs.xfs(8), xfs_admin(8), xfs_check(8), xfs_copy(8), xfs_logprint(8),
xfs_ncheck(8), xfs_repair(8), mount(8), chmod(2), mknod(2), stat(2),
xfs(5).
xfs_db(8)
Man(1) output converted with
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This page was generated on Sat Sep 8 16:40:38 GMT 2007
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